1. Recipes for Use With Thin Clients
Dave Ensor
BMC Software

2. Agenda Introduction Issues Conclusions Key Choices for Web Deployment
Remember Client/Server?
Current Best Practice
300% Java examined
Planning Server Distribution
Conclusions

3. Introduction Application Architecture? It’s the web Three easy pieces
“Run anywhere”
Ease of use
Three easy pieces
Browser
Web Server
Data Server
Now the problems begin
Data Management
Presentation Management
Application Logic

4. Architectural Issues I
Intranet or Extranet or Internet?
Has fundamental impact on other choices
Browser
Make & Version Independence
Security
Firewall?
DMZ?

5. Net Worlds The Internet An Extranet An Intranet Fire Wall Customers
Local Users
Stock
Suppliers
Orders

6. Architectural Issues II
Web Server
Oracle Instance
Oracle Application Server
Other
Programming Language
At the interface
(D)HTML, JavaScript
In the middle
Java Servlets
In the database
Java, PL/SQL

7. Deployment Choices Web servers How many? Data Servers Distributed?
Distribution algorithm
Functional
Geographic
Data Servers
Distributed?
Clustered?
Fail-safe?

8. Remember Client/Server?
Two drivers
Desire to leverage cheap desktop devices
Desire for Graphical User Interfaces (GUI’s)
Apparently a winning combination
Desktop manages the pixels
Server manages the data
Where to run application logic?
Stock

9. Expectations for Distribution
Lower Cost
Faster Response
Greater Availability
Greater Control
Greater Throughput
The reality was different

10. Network Limits The major problems Bandwidth Packet rates
Web more so than Client/Server
Packet rates
Message round trip times
The solutions
Hardware & Software Improvements
Encapsulation
Architectural Improvements

11. Bandwidth Typical screen entry < 100 Typical screen data ~ 2K ?
Typical server messages ~ 10k ?
Typical Java Applet ~ 200k ?
>= MHz
10 MHz
100 Mhz

12. Packet Rates
Per card
Perhaps 1,500/second

13. Message Round Trip Times
500 msec
~2 msec
~1 msec

14. * plus network load for message transfer
Load Distribution
Load
Presentation Management
High*
in short bursts
Application Logic
Low*
can be increased through design
High*
and typically continuous
Data Management
* plus network load for message transfer

15. Presentation Management
Load Distribution
Presentation Management
Message Passing
Message Passing
Application Logic
Message Passing
Message Passing
Data Management
Not to scale

16. Current Best Practice Interface Layout (& Logic?)
Three tier architecture
Interface Layout (& Logic?)
Conventional App, Applet (D)HTML + JavaScript
Application Logic within
Dedicated Web Server
Transaction Manager
DBMS Packaged Procedures
Data Management Logic
Triggers
Declarative Constraints
Interface
Application
Data Management
Browser
Web Server
Data Server

17. Current Best Practice Interface Layout (& Logic?) Application Logic
Encapsulate & Separate
Interface Layout (& Logic?)
Application Logic
Data Management Logic
Minimize Network Traffic
Limit
Process Counts
Connection Counts
Interface
Application
Data Management

18. Three tier architectures
Markedly superior at handling heterogeneity
Across the interfaces
No longer an issue!
Across the data servers
Sybase
Windows
Windows CE
Oracle
Motif
IMS/DB
Embedded

19. 300% Java Examined Java on the client
Should be the exception rather than the rule
Java on the App Server
Potentially a good choice
Java on the Data Server
PL/SQL still the language of choice for embedded SQL?
Total
100%
~10%
100%
~75%
100%
~10%
300%
<100%

20. Applet Avoidance HTML Capable of presenting most data clearly XML
Overcomes most of the issues with HTML
Only operable in the latest browser releases
DHTML and JavaScript
Not as pure as an applet
But much less to download
Allows local validation

21. Client-side Logic How far can you get with just HTML?
Anywhere with an airport!
So when do you need Java at the client?

22. Using win32 calls Necessary? Desirable? More is possible But is it
Interactive design may have to be re-learnt to completely avoid it …

23. … much the same is possible in Java

24. Key questions OK, Mr Architect. You’re a smart guy.
Tell me some advantages of complex client-side validation
Then tell me some advantages of other client-side application logic

25. Planning Server Distribution
Between Browsers and App Servers
Only two cases
LAN
High bandwidth, fast round trips
WAN
Distance is not a problem
Round trip times & bandwidth are major issues
Between App Servers and Data Servers
Normal rules apply
Minimize network traffic
Place high volumes on “short” network paths

26. Planning Server Distribution
Navigation between App Servers via HTML Links
Multiple Databases can work well
Single Physical Site may be an advantage

27. Failure Resilience App Servers scale well The paradox The answer
cookies can ease failover issues
The paradox
The web is absolutely 365*24*7
Database outages are still required
e.g. logical schema changes
The answer
The application must cope
Pended transactions?
Allowable failure rate?

28. Conclusions Use web technology Put application rules on servers
A middle tier is inevitable
But it can share hardware
KISS
Keep the client thin e.g. HTML
Control the message traffic
Between client & server
Between cooperating servers
Leverage the paradigm shift in the interface
Web Server
Data Server
Browsers